Nitric oxide (NO) is synthesized enzymatically from arginine in numerous tissues and cell types by a family of enzymes, collectively known as nitric oxide synthase (NOS, E.C. 1.14.13.39). Three principal isoforms of this enzyme have been isolated and characterized, each associated with different physiological functions: the immune response (inducible NOS or iNOS), smooth muscle relaxation (endothelial NOS or eNOS), and neuronal signaling (neuronal NOS or nNOS). All of these isoforms utilize NADPH, FAD, FMN, (6R)-5,6,7,8-tetrahydrobiopterin and heme as cofactors.
Overproduction of NO has been a factor in numerous disease states. NO overproduction by nNOS has been implicated in strokes, migraine headaches, Alzheimer's disease, and with tolerance to and dependence on morphine. iNOS-mediated overproduction of NO has been associated with development of colitis, tissue damage and inflammation, and rheumatoid arthritis.
Animal studies and early clinical trials suggest that NOS inhibitors could be therapeutic in many of these disorders; however, because of the importance of nitric oxide to physiological functioning, potent as well as isoform-selective inhibitors are essential. nNOS inhibition has been targeted for treatment of strokes, and iNOS inhibition for the treatment of septic shock and arthritis. Although there may be pathologies associated with overactivity of eNOS, blood pressure homeostasis is so critical that most investigators believe that therapeutically useful NOS inhibitors should not inhibit eNOS.
Excellent inhibitory potency and selectivity for nNOS over eNOS and iNOS have been achieved with certain prior art (FIG. 1) nitroarginine dipeptide amides that have an amine-containing side chain (1-3). See Huang, H.; Martasek, P.; Roman, L. J.; Masters, B. S. S.; Silverman, R. B. Nω-Nitroarginine-Containing Dipeptide Amides. Potent and Highly Selective Inhibitors of Neuronal Nitric Oxide Synthase. J. Med. Chem. 1999, 42, 3147-53.
The most potent nNOS inhibitor among these compounds is L-ArgNO2-L-Dbu-NH2 (1) (Ki=130 nM), which also shows excellent selectivity over eNOS (>1500-fold) and 192-fold selectivity over iNOS. Further, peptidomimetic modifications are, however, invariably necessary before such compounds can be therapeutically useful. Generally, peptides have poor bioavailability and are generally unsuccessful drug candidates.
The foregoing background information, together with other aspects of the prior art, is described more fully and better understood in light of the following publications: (1) Kerwin, J. F., Jr.; Lancaster, J. R., Jr. Nitric Oxide; A New Paradigm for Second Messengers. Med. Res. Rev. 1994, 14, 23-74; (2) Kerwin, J. F., Jr.; Heller, M. The Arginine-Nitric Oxide Pathway: A Target for New Drugs. J. Med. Chem. 1995, 38, 4342-62; (3) Stuehr, D. J.; Griffith, O. W. Mammalian Nitric Oxide Synthases. Adv. Enzymol. Relat. Areas Mol. Biol. 1992, 65, 287-346; (4) MacMicking, J.; Xie, Q. W.; Nathan, C. Nitric Oxide and Macrophage Function. Annu. Rev. Immunol. 1997, 15, 323-50; (5) Forstermann, U.; Pollock, J. S.; Schmidt, H. H. H. W.; Heller, M.; Murad, F. Calmodulin-Dependent Endothelium-Derived Relaxing Factor/Nitric Oxide Synthase Activity is Present in the Particulate and Cytosolic Fractions of Bovine Aortic Endothelial Cells. Prot. Natl. Acad. Sci. U.S.A. 1991, 88, 1788-92; (6) Schmidt, H. H. H. W.; Walter, U. NO at Work. Cell 1994, 78, 919-25; (7)(a) Choi, D. W.; Rothman, S. M. The role of glutamate neurotoxicity in hypoxic-ischemic neuronal death. Annu. Rev. Neurosci. 1990, 13, 171-82; (b) Garthwaite, J. In the NMDA Receptor; Watkins, J. C. Collingridge, G. L., Eds.; Oxford University Press.; Oxford, England, 1989; pp 187-205; (8) Thomson, L. L.; Iversen, H. K.; Lassen, L. H.; Olesen, J. The role of nitric oxide in the migrane pain. CNS Drugs 1994, 2, 417-22; (9) Dorheim, M. A.; Tracey, W. R.; Pollock, J. S.; Grammas, P. Nitric Oxide synthase activity is elevated in brain microvessels in Alzheimer's disease. Biochem. Biophys. Res. Commun. 1994, 205, 659-65; (10) Bhargava, H. N. Attenuation of tolerance to, and physical dependence on, morphine in the rat by inhibition of nitric oxide synthase. Gen. Pharmacol. 1995, 26, 1049-53; (11) Seo, H. G.; Takata, I.; Nakamura, M.; Tatsumi, H.; Suzuki, K.; Fujii, J.; Taniguchi, N. Introduction of nitric oxide and concommittant suppression of superoxide dismutase in experimental colitis in rats. Arch. Biochem. Biophys. 1995, 324, 41-7; (12) Kubes, P.; Suzuki, M.; Granger, D. N. Nitric Oxide; an endogeneous modulator of leukocyte adhesion. Proc. Natl. Acad. Sci. U.S.A. 1991, 88, 4651-5; (13) Maclintyre, I.; Zaidi, M.; Towhidul Alam, A. S. M.; Datta, H. K.; Moonga, B. S.; Lidbury, P. S.; Hecker, M.; Vane, J. R. Osteoclastic inhibition; an action of nitric oxide not mediated by cyclic GMP. Proc. Natl. Acad. Sci. U.S.A. 1991, 88, 2936-40; (14) Kilbourn, R. G.; Jubran, A.; Gross, S. S.; Griffith, O. W.; Levi, R.; Adams, J.; Lodato, R. F. Reversal of endotoxin-mediated shock by NG-methyl-L-arginine, an inhibitor of nitric oxide synthesis. Biochem. Biophys. Res. Commun. 1990, 172, 1132-8; (15)(a) Collins, J. L.; Shearer, B. G.; Oplinger, J. A.; Lee, S.; Garvey, E. P.; Salter, M.; Duffy, C.; Burnette, T. C.; Furfine, E. S, N-Phenylamidines as selective inhibitors of human neuronal nitric oxide synthase. Structure-activity studies and demonstration of in vivo activity. J. Med. Chem. 1998, 41. 2858-71; (16) Wright, C. W.; Rees, D. D.; Moncada, S. Protective and Pathological roles of nitric oxide in endotoxin shock. Cardiovasc. Res. 1992, 26, 48-57; (17) Garvey, E. P.; Oplinger, J. A.; Furfine, E. S.; Kiff, R. J.; Laszlo, F.; Whittle, B. J. R.; Knowles, R. G. 1400W is a slow, tight binding, and highly selective inhibitor of inducible nitric oxide synthase in vitro and in vivo. J. Biol. Chem. 1997, 272, 4959-63; (18) Huang, H; Martasek, P.; Roman, L. J.; Masters, B. S. S.; Silverman, R. B. Nω-Nitroarginine-Containing Dipeptide Amides. Potent and Highly Selective Inhibitors of Neuronal Nitric Oxide Synthase. J. Med. Chem. 1999, 42, 3147-53.